'use strict';
var single_element = function(collection){
    let arr = collection.filter(function(element,index,collection){
        return index%2 !== 0;
    })
    
    let result = [];
    for(let item of arr){
        if( arr.indexOf(item)===arr.lastIndexOf(item)){
            result.push(item);
        }
    
        
    }
    console.log(result);
    return result;
    };
    single_element( [1, 2, 3, 2, 5, 6, 21, 43, 12, 5]);
    single_element( [11, 11, 22, 11, 33, 11]);
    module.exports = single_element;
    